Re: And another crm114 script language question about 'isolate'

On Mon, Mar 31, 2008 at 07:10:34AM +0100, Ger Hobbelt wrote:
> Ja-a-a-aaa, so far with you all the way. But-t-t-t lemme rephrase: the
> wonder starts (started, I should say) here:
> 
> {
>     window
>     isolate (:a:)           # --> 'a'
>     output /a = ':*:a:'\n/  #
>     isolate (:a:) /foo/     # --> 'foo' (override; old 'a' is lost
>     output /a = ':*:a:'\n/  #
>     isolate <default> (:a:) /bar/  # --> in this case, :a: will _stay_ 'foo'
>     output /a = ':*:a:'\n/  #
>     isolate (:a:)
>     output /a = ':*:a:'\n/  # now what do you expect here? Then run
> and see if reality matches brain. For me it didn't.
> }
> 
> (source attached)
> 
> Please think about the last isolate before you check and run it: this
> is a perception check after all.

I get:

a = ''		# ok, no val assigned yet
a = 'foo'	# ok, re-isolate + val-assign
a = 'foo'	# ok, not touched because of <default> 
a = 'foo'	# ok, just re-isolate, but don't bother the value 

looks alright to me.

> I have learned the hard way that I had forgotten something important
> about 'isolate' and why it is called exactly that ('isolate', and not,
> say, 'instantiate', 'declare' or 'allocate')

yeah ;) - note the last ISOLATE: you'd do just that after a MATCH (:: :a:) ...
if you'd like to save :a: and its value. If you redo it, it checks if it's 
already there and ISOLATE'd, then skip if yes.

In diagrams (showing just values):

 main buffer         : .............foo..........
 var :x:             :      ^----------------^

after MATCH (:: :a:) [:x:] /foo/
 
 string buffer       : .............foo..........
 var :x:             :      ^----------------^
 var :a:             :              ^-^

now :a: is bound to :x:, if you change :x: you (may) change :a: as well; if
you change :a: you do change :x: as well.

after ISOLATE (:a:) - unbind :a: from :x: :
 
 string buffer: .............foo..........
 var :x:      :      ^----------------^

 other/isolate buffer: .............foo............
 var :a:             :              ^-^

ISOLATE (:a:) - again wouldn't do anything at this point;
ISOLATE <default> (:a:) /bar/ - wouldn't be allowed to change val;
ISOLATE (:a:) /bar/ - would only need to change the value;
ALTER (:x:) // - would change just :x:
ISOLATE (:x:) // - likewise
ALTER (:a:) // - would change just :a:


HTH
-- 
paolo

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